Low-Coupling Oxide Media (LCOM)

ABSTRACT

A low-coupling perpendicular magnetic recording media comprising a magnetic storage layer and at least one low saturation magnetization layer. The magnetic storage layer has a saturation magnetization between about 400-900 emu/cm3 and the at least one low saturation magnetization layer has a saturation magnetization below that of the magnetic storage layer.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority of U.S.patent application Ser. No. 12/272,662, filed Nov. 17, 2008, the contentof which is hereby incorporated by reference in its entirety.

BACKGROUND

Magnetic discs with magnetizable media are used for data storage in mostcomputer systems. According to the domain theory, a magnetic material iscomposed of a number of submicroscopic regions called domains. Eachdomain contains parallel atomic moments and is magnetized to saturation,but the directions of magnetization of different domains are notnecessarily parallel. In the absence of an applied magnetic field,adjacent domains may be oriented randomly in any number of severaldirections, called the directions of easy magnetization, which depend onthe geometry of the crystal. The resultant effect of all these variousdirections of magnetization may be zero, as is the case with anunmagnetized specimen. When a magnetic field is applied, the domainsmost nearly parallel to the direction of the applied field grow in sizeat the expense of the others. This is called boundary displacement ofthe domains or domain growth. A further increase in magnetic fieldcauses more domains to rotate and align parallel to the applied field.When the material reaches the point of saturation magnetization, nofurther domain growth would take place on increasing the strength of themagnetic field.

The ease of magnetization or demagnetization of a magnetic materialdepends on the crystal structure, grain orientation, the state ofstrain, and the direction and strength of the magnetic field. Themagnetization is most easily obtained along an easy axis ofmagnetization and most difficult along the hard axis of magnetization. Amagnetic material is said to possess a magnetic anisotropy when easy andhard axes exist. On the other hand, a magnetic material is said to beisotropic when there are no easy or hard axes.

Many prior art magnetic recording media were fabricated with alongitudinal configuration. That is, the recording media were fabricatedwith in-plane (longitudinal) anisotropy in the magnetic layer.Longitudinal anisotropy results in magnetization forming in a directionin a plane parallel to the surface of the magnetic layer.

The demand for higher capacity magnetic recording media, however, hasresulted in interest in perpendicular recording media; that is,recording media with a perpendicular anisotropy in the magnetic layerresulting in magnetization forming in a direction perpendicular to thesurface of the magnetic layer. Typically, perpendicular recording mediaare fabricated with a polycrystalline CoCr alloy or CoPt-oxide alloyfilm. Co-rich areas in the polycrystalline film are ferromagnetic whileCr or oxide rich areas in the film are non-magnetic. Magneticinteraction between adjacent ferromagnetic domains are attenuated by thenon-magnetic areas in between.

SUMMARY

One embodiment of this invention relates to a low-coupling perpendicularmagnetic recording media comprising a magnetic storage layer and atleast one low saturation magnetization layer, wherein the magneticstorage layer has a saturation magnetization between about 400-900emu/cm³ and the at least one low saturation magnetization layer has asaturation magnetization below that of the magnetic storage layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood by reference to theDetailed Description of the Invention when taken together with theattached drawings, wherein:

FIG. 1 shows a magnetic recording medium according to one embodiment ofthe invention.

FIG. 2 shows a magnetic recording medium according to another embodimentof the invention.

FIG. 3 shows a magnetic recording medium according to a third embodimentof the invention.

FIG. 4 shows a magnetic recording medium according to a fourthembodiment of the invention.

FIG. 5 illustrates Monte Carlo simulations demonstrating improvedrecording properties of an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

As used in the specification and claims, the singular forms “a”, “an”and “the” include plural references unless the context clearly dictatesotherwise.

The inventors have discovered that a weak uniform direct exchangecoupling between magnetic grains in perpendicular recording mediaprovides improved performance. The inventors have further discoveredthat weak uniform direct exchange coupling between the magnetic grainsmay be produced by adding a low saturation magnetization magneticlayer(s) in the perpendicular media structure. The inventors haveadditionally discovered that the strength of the direct exchangecoupling can be controlled by varying saturation magnetization (M_(s))of the magnetic layer.

An embodiment of this invention relates to a low-coupling perpendicularmagnetic recording media comprising at least one low saturationmagnetization layer, wherein the at least one low saturationmagnetization layer has a saturation magnetization below 600 emu/cm³.

Another embodiment of the invention relates to a method of making alow-coupling perpendicular magnetic recording media comprisingdepositing an adhesion layer on a substrate, depositing a softunderlayer, depositing an non-magnetic interlayer, depositing a storagelayer; and depositing a low saturation magnetization magnetic layer,wherein the at least one low saturation magnetization layer has asaturation magnetization below 600 emu/cm³.

Another embodiment of the invention relates to a method comprisingobtaining a storage media having at least one layer with a saturationmagnetization below

Additional advantages of this invention will become readily apparent tothose skilled in this art from the following detailed description,wherein only a selection of preferred embodiments of this invention areshown and described, to illustrate the best modes contemplated forcarrying out this invention. As will be realized, this invention maycomprise other and different embodiments, and its details are capable ofmodifications in various obvious respects, all without departing fromthis invention. Accordingly, the drawings and description are to beregarded as illustrative in nature and not as restrictive.

EXAMPLES

All samples described in this disclosure were fabricated with DCmagnetron sputtering except carbon films. Example data demonstrating thereduction of exchange coupling by reactive sputtering are explainedherein.

FIG. 1 illustrates a first preferred embodiment of the invention. Thelow-coupling perpendicular magnetic recording media 10 of thisembodiment includes a substrate 11, an adhesion layer 12, a soft underlayer 13, an amorphous layer 14, a non-magnetic interlayer 15, alow-coupling magnetic layer 16, a storage layer 17, and a carbonprotective overcoat. Optionally, the soft under layer 13, the amorphouslayer 14, the non-magnetic interlayer 15, the low-coupling magneticlayer 16, the storage layer 17, and the carbon protective overcoat 18may comprise multiple layers.

Preferred materials for the optional adhesion layer 12 include alloyscontaining one or more of Cr, Ni, Ta, and Ti. The choice depends on thesubstrate 11 and the material selected for the soft underlayer 13 and iswithin the skill of one of ordinary skill in the art. Preferably, thethickness of the adhesion layer is about 1-400 nm. More preferably, thethickness is about 2-20 nm.

Preferred materials for the soft underlayer 13 include alloys of atleast one of Fe and Co with one or more elements selected from Ni, B, P,Si, C, Zr, Nb, Hf, Ta, AI, Si, Cu, Ag, Au. Preferably, the thickness ofthe soft underlayer 13 is about 10-400 nm. More preferably, thethickness is about 20-100 nm.

The amorphous layer 14 is optional. Preferred materials for theamorphous layer 14 include elements and alloys comprising Ta, Ti, Ni,Cr, Zr, Nb, and P, in compositions for which these alloys are amorphous.Other preferred materials include amorphous ferromagnetic materialsconsisting of Fe with one or more elements selected from Co, B, P, Si,C, Zr, Nb, Hf, Ta, AI, Si, Cu, Ag, and Au. Still other preferredmaterials include Ti_(x)Cr_(100-x) and Ta_(x)Cr_(100-x), where(30<x<60). Preferably, the thickness of the amorphous layer 14 is about0-10 nm. More preferably the thickness is about 0.2-4 nm.

The crystallographic structure of the non-magnetic interlayer 15 dependson the crystallographic structure of the storage layer 17. For example,if the storage layer 17 is made of a Co-rich alloy with a hexagonalclosed packed (hcp) structure, the non-magnetic interlayer 15 mayinclude a face-centered cubic (fcc) layer of Cu, Ag, Au, Ir, Ni, Pt, Pd,or their alloys. Preferably, the thickness of this non-magneticinterlayer 15 ranges from about 0.2 nm to about 40 nm. More preferably,the thickness is about 1-20 nm. Alternatively, the non-magneticinterlayer 15 may include a hexagonal closed packed (hcp) layer of Ru,Re, Hf, Ti, Zr, or their alloys. Other hcp layers that may be usedinclude Co and CoCr alloys. Optional additives to CoCr include Ta, B,Pt, Nb, Ru, Zr, and oxide materials. To use CoCr, the concentration ofCr and other alloying elements is chosen so that the alloy isnon-magnetic and has an hcp crystal structure. To use Co-containingalloys the concentration of Cr and other alloying elements is chosen sothat the alloy is non-magnetic and has an hcp crystal structure.Preferably, the thickness of the hcp layer(s) ranges from about 0.2 nmto 40 nm. More preferably, the thickness is about 1-20 nm.

The storage layer 17 may comprise one layer or any number of layers ofmagnetic material. Preferred materials for the storage layer 17 includeCo with one or more elements selected from Pt, Cr, Ta, B, Cu, W, Mo, Ru,Ni, Nb, Zr, Hf. Optionally, one or more oxides of elements such as Si,Ti, Zr, AI, Cr, Co, Nb, Mg, Ta, W, or Zn may also be present in thestorage layer 17. Preferably, the storage layer 17 is grown in acontrolled atmosphere. Preferably, the controlled atmosphere includesAr, Kr, or Xe or combination of these gasses with a reactive gascomponent such as O2. The storage layer 17 may be grown at lowtemperatures, i.e. below 400 K. Typically, low temperatures are used forfabricating magnetic layers sputtered in controlled atmospheresincluding combinations of Ar, Kr, Xe and O₂. Alternatively, the storagelayer 17 may be grown at elevated temperatures, i.e. above 400 K.Preferably, the elevated temperature is higher than 420 K and below 600K.

In the present embodiment, the low-coupling magnetic layer 16 is locatedbetween non-magnetic interlayer 15 and the storage layer 17. In thisembodiment, the crystallographic structure of the low-coupling magneticlayer 16 may be adjusted to improve the crystallographic growth of thestorage layer 17. For example, for a storage layer(s) 17 with an hcpcrystallographic structure, a low-coupling magnetic layer(s) 16 may beselected to have an hcp or fcc crystallographic structure, or it may beamorphous. Preferred materials for the low-coupling magnetic layer 16include at least one of Fe, Co, Ni with one or more elements selectedfrom Cr, Pt, Ta, B, Ru, Cu, Ag, Au, W, Mo, Nb, Zr, Hf, Ti, Zn, and Re.Preferably, the low-coupling magnetic layer 16 has a lower Ms than theMs of the storage layer 17 to obtain weak direct exchange coupling. Thestorage layer 17 preferably has a Ms of approximately 400-900 emu/cm³.The low-coupling magnetic layer 16 preferably has a Ms less than orequal to about 600 emu/cm³. More preferably Ms is less than or equal toabout 300 emu/cm³. Even more preferably, Ms is less than or equal toabout 50 emu/cm³. Possible storage layer 17/low-coupling magnetic layer16 combinations may be, but are not limited to: 600/300, 900/600,500/50, 450/350, 600/450 and 900/400.

The topmost layer covering the low-coupling perpendicular magneticrecording media 10 of this embodiment is the carbon protective overcoat18. The thickness of the carbon protective overcoat 18 may varyaccording to the desired life and durability of the low-couplingperpendicular magnetic recording media 10.

FIG. 2 illustrates a second preferred embodiment of the invention. Thelow-coupling perpendicular magnetic recording media 20 of thisembodiment includes a substrate 11, an adhesion layer 12, a soft underlayer 13, an amorphous layer 14, an non-magnetic interlayer 15, astorage layer 17, a low-coupling magnetic layer 16, and a carbonprotective overcoat. That is, in contrast to the first embodiment, thelow-coupling magnetic layer 16 is between the storage layer 17 and thecarbon protective overcoat. Further, as in the first embodiment, thesoft under layer 13, the amorphous layer 14, the non-magnetic interlayer15, the storage layer 17, the low-coupling magnetic layer 16, and thecarbon protective overcoat 18 may include multiple layers.

FIG. 3 illustrates a third preferred embodiment of the invention. Thelow-coupling perpendicular magnetic recording media 30 of thisembodiment includes a substrate 11, an adhesion layer 12, a soft underlayer 13, an amorphous layer 14, an non-magnetic interlayer 15, a firstlow-coupling magnetic layer 16 a, a storage layer 17, a secondlow-coupling magnetic layer 16 b, and a carbon protective overcoat. Incontrast to the first embodiment, the low-coupling magnetic layer 16comprises at least two layers that are separated by at least one storagelayer 17. Further, the soft underlayer 13, the amorphous layer 14, thenon-magnetic interlayer 15, the first low-coupling magnetic layer 16 a,the storage layer 17, the second low-coupling magnetic layer 16 b, andthe carbon protective overcoat 18 may include multiple layers.

FIG. 4 illustrates a fourth preferred embodiment of the invention. Thelow-coupling perpendicular magnetic recording media 30 of thisembodiment includes a substrate 11, an adhesion layer 12, a soft underlayer 13, an amorphous layer 14, an non-magnetic interlayer 15, alow-coupling magnetic layer 16, a first storage layer 17 a, a secondstorage layer 17 b, and a carbon protective overcoat. In contrast to thefirst embodiment, the storage layer 17 comprises at least two layersthat are separated by at least one low-coupling magnetic layer 16.Further, the soft underlayer 13, the amorphous layer 14, thenon-magnetic interlayer 15, the first low-coupling magnetic layer 16,the first storage layer 17 a, the second storage layer 17 b, and thecarbon protective overcoat 18 may include multiple layers.

FIG. 5 illustrates Monte Carlo simulations demonstrating improvedrecording properties of an embodiment of the invention having a thicklow-coupling magnetic layer of hcp crystallographic structure withM_(s)=50 emu/cm³ located between a non-magnetic interlayer 15 and astorage layer 17. In particular, the Monte Carlo simulations illustratedin FIG. 5 show that optimal recording properties of perpendicular mediacan be achieved for media with very low and uniform direct exchangecoupling (A*), wherein A* comprises a value of A*≈(0.05±0.03)*10¹¹ J/m(FIG. 5). Such a low value of direct exchange coupling results from mostsputtered Co-alloy thin films having low saturation magnetization in arange of about 50 emu/cc<M_(s)<300 emu/cc. Assumptions for thesimulations include: a grain size dispersion of σ_(D)/D≈0.1, whereσ_(D)/D describes a microstructure comprising a grain size defined by anaverage grain diameter (D) and a variation of grain size defined by astandard deviation (σ_(D)); anisotropy dispersion σ_(HA)/H_(A)≈0.02,where H_(A) is the average anisotropy field of grains comprising themedia and σ_(HA) is the standard deviation of the anisotropy field; andlinear density of 1270 kfci. Approximate values of σ_(D)/D andσ_(HA)/H_(A) can be experimentally obtained by microscopy techniquessuch as TEM and SEM, and magnetometry techniques such as Berger's methodand AC transverse susceptibility respectively. Linear density is simplyrelated to the length of each bit that is controlled by the recordingprocess.

Similar model result trends to those shown for the specified modelcalculation parameters are obtained for a range of values of the modelcalculation parameters. Based on the results of the simulations, theinventors have determined that an additional low magnetization magneticlayer(s) 16 in perpendicular media structure provides lower exchangecoupling between magnetic layers and grains in perpendicular media,which will significantly improve the performance. By varying M_(s) ofthe low magnetization magnetic layer 16, the strength of direct exchangecoupling in perpendicular recording media can be controlled. Simulationsdemonstrate that the location of the low magnetization magnetic layer 16can be between the non-magnetic interlayer 15 and the storage layer 17,or between the storage layer 17 and the carbon protective overcoat 18.Alternatively, the low magnetization magnetic layer 16 may be locatedbetween or adjacent to a plurality of storage layers 17, e.g., 17 a and17 b shown in FIG. 4. Alternatively, the low magnetization magneticlayer 16 may comprise a plurality of low magnetization layers, such aslayers 16 a, 16 b shown in FIG. 3, which can be located between theinterlayer 15 and the storage layer 17 and between the storage layer 17and the carbon protective overcoat 18. Preferably, M_(s) of lowmagnetization magnetic layer 16 is low, i.e. below about 600 emu/cm³ toprovide low exchange coupling. More preferably, M_(s) is below about 300emu/cm³. Even more preferably, M_(s) is below about 50 emu/cm³. Theimplementations described above and other implementations are within thescope of the following claims.

1. An apparatus comprising: a first magnetic storage layer; a secondmagnetic storage layer; and a low saturation magnetization layer betweenthe first magnetic storage layer and the second magnetic storage layer,the low saturation magnetization layer having a saturation magnetizationlevel below that of the first and second magnetic storage layers.
 2. Theapparatus of claim 1 wherein the low saturation magnetization layer hasa saturation magnetization level below that of the first and secondmagnetic storage layers by at least about 100 emu/cm³.
 3. The apparatusof claim 2 wherein the low saturation magnetization layer has asaturation magnetization level less than or equal to about 300 emu/cm³.4. The apparatus of claim 1 wherein the low saturation magnetizationlayer has a saturation magnetization level below that of the first andsecond magnetic storage layers by at least about 250 emu/cm³.
 5. Theapparatus of claim 4 wherein the low saturation magnetization layer hasa saturation magnetization level less than or equal to about 50 emu/cm³.6. The apparatus of claim 1 wherein each of the first magnetic storagelayer and the second magnetic storage layer comprises a magnetic layercomprising Co and one or more elements selected from the groupconsisting of Pt, Cr, Ta, B, Cu, W, Mo, Ru, Ni, Nb, Zr, Hf.
 7. Theapparatus of claim 1 wherein each of the first magnetic storage layerand the second magnetic storage layer comprises one or more oxidesselected from group consisting of oxides of Si, Ti, Zr, Al, Cr, Co, Nb,Mg and Zn.
 8. The apparatus of claim 1 wherein the low saturationmagnetization layer comprises at least one of Fe, Co, or Ni with one ormore elements selected from the group consisting of Cr, Pt, Ta, B, Ru,Cu, Ag, Au, W, Mo, Nb, Zr, Hf, Ti, Zn, and Re.
 9. An apparatuscomprising: a first low saturation magnetization magnetic layer; asecond low saturation magnetization magnetic layer; and a magneticstorage layer between the first low saturation magnetization magneticlayer and the second low saturation magnetization magnetic layer, themagnetic storage layer having a saturation magnetization level abovethat of the first and second low saturation magnetization magneticlayers.
 10. The apparatus of claim 9 wherein the magnetic storage layerhas a saturation magnetization level above that of the first and secondlow saturation magnetization magnetic layers by at least about 100emu/cm³.
 11. The apparatus of claim 9 wherein the magnetic storage layerhas a saturation magnetization level above that of the first and secondlow saturation magnetization magnetic layers by at least about 250emu/cm³.
 12. The apparatus of claim 9 wherein the magnetic storage layercomprises a magnetic layer comprising Co and one or more elementsselected from the group consisting of Pt, Cr, Ta, B, Cu, W, Mo, Ru, Ni,Nb, Zr, Hf.
 13. The apparatus of claim 9 wherein the magnetic storagelayer comprises one or more oxides selected from group consisting ofoxides of Si, Ti, Zr, Al, Cr, Co, Nb, Mg and Zn.
 14. The apparatus ofclaim 9 wherein each of the low saturation magnetization layerscomprises at least one of Fe, Co, or Ni with one or more elementsselected from the group consisting of Cr, Pt, Ta, B, Ru, Cu, Ag, Au, W,Mo, Nb, Zr, Hf, Ti, Zn, and Re.
 15. A magnetic recording mediumcomprising: a first low saturation magnetization magnetic layer; asecond low saturation magnetization magnetic layer; and a perpendicularmagnetic storage layer between the first low saturation magnetizationmagnetic layer and the second low saturation magnetization magneticlayer, the perpendicular magnetic storage layer having a saturationmagnetization level above that of the first and second low saturationmagnetization magnetic layers.
 16. The magnetic recording medium ofclaim 15 wherein the perpendicular magnetic storage layer has asaturation magnetization level above that of the first and second lowsaturation magnetization magnetic layers by at least about 100 emu/cm³.17. The magnetic recording medium of claim 15 wherein the perpendicularmagnetic storage layer has a saturation magnetization level above thatof the first and second low saturation magnetization magnetic layers byat least about 250 emu/cm³.
 18. The magnetic recording medium of claim15 wherein the perpendicular magnetic storage layer comprises a magneticlayer comprising Co and one or more elements selected from the groupconsisting of Pt, Cr, Ta, B, Cu, W, Mo, Ru, Ni, Nb, Zr, Hf.
 19. Themagnetic recording medium of claim 15 wherein the perpendicular magneticstorage layer comprises one or more oxides selected from groupconsisting of oxides of Si, Ti, Zr, Al, Cr, Co, Nb, Mg and Zn.
 20. Themagnetic recording medium of claim 15 wherein each of the low saturationmagnetization layers comprises at least one of Fe, Co, or Ni with one ormore elements selected from the group consisting of Cr, Pt, Ta, B, Ru,Cu, Ag, Au, W, Mo, Nb, Zr, Hf, Ti, Zn, and Re.